This invention relates to a surface and interface analysis technique, and in particular, it relates to a surface analysis method suitable for nondestructive and high-precision depth profile analysis, and an apparatus therefor.
With increasing packing density and decreasing film thickness of semiconductor devices, depth profile analysis (as well as small area analysis) has become very important.
Chemical state of a Si/SiO.sub.2 interface determines the electric characteristic of an MOS transistor, and that of a polySi/SiO.sub.2 or polySi/Si.sub.3 N.sub.4 interface has an influence on the electric characteristic of a capacitor. The electric characteristics of transistors and capacitors can be greatly improved by these (abruption in an interface, and a distribution and change of elements and chemical bonds in the vicinity of an interface), analyzing these chemical states and feeding the results back to a production process. Also, in a photo-CDV process, the distribution of film-forming metals, such as W, Ti, etc., near the surface is very important.
In the above examples, elements and chemical bonds to be analyzed exist in a region with a depth from a sample surface of a few to several tens nm. Hence, surface analysis technique necessary for analyzing them is required to have capability of analyzing atomic species and their chemical bonds or changes in their compositions in a region from the top surface of a sample to its several tens nm deep interior part. Also, the surface analysis technique is required to achieve a depth resolution of about 0.1 nm in case that an interface abruptly changes in its structure or composition and so on. It goes without saying that the technique is required to be nondestructive.
Conventional depth profile analysis techniques are as follows. One of the well-known techniques is AES (Auger Electron Spectroscopy) or SIMS (Secondary Ion Mass Spectroscopy). These techniques carry out depth profile analysis by irradiating a sample surface with ions having a large kinetic energy for sputtering the surface, and analyzing the surface or sputtered particles. The other techniques are EDX (Energy Dispersion X-ray Spectroscopy) and PIXE (Particle Induced X-ray Emission), in which depth profile analysis is carried out by irradiating the surface with particle beams and measuring intensity attenuation caused by absorption of emitted X-ray by the sample.
The above prior techniques have the following problems.
One of the problems is cascade mixing found in an ions-sputtering method. Within a region irradiated with ions (a region from an irradiated surface to a 1 to 10 nm deep interior part), due to the above effect, element distribution tends to be uniform. Therefore, it is impossible to obtain any depth profiles in this region. In addition to this cascade mixing, the ion-sputtering method has other various factors to decrease analysis accuracy, such as a preferential sputtering caused by a difference in atomic species, crater edge effect caused by non-uniformity of ion beams, etc. As a result, the depth resolutions in AES and SIMS are limited to 1 nm [C. W. Magee and R. E. Honig, Surf. Interface Anal. 4, 35 (1982)]. Furthermore, AES and SIMS have problems that chemical bond analysis is almost impossible and that the analysis is destructive.
On the other hand, EDX and PIXE are only applicable to depth profile analysis of a sample with layered structures (an element distribution within the layer is uniform), and their depth resolution is about 5 nm. EDX and PIXE therefore have a low resolution, and furthermore, they do not make it possible to carry out depth profile analysis of elements whose distribution continuously changes.
As mentioned above, the prior art methods has a low depth resolution, and no accurate depth profiles can be measured. Furthermore, the prior art methods also have a disadvantage that the chemical bond analysis is impossible.